Sorbent compositions having pneumatic conveyance capabilities

ABSTRACT

Sorbent compositions including sorbent particles of a small particle sized sorbent with increased pneumatic conveyance properties. The sorbent compositions have relatively small median particle size and have a controlled particle size distribution (PSD). Specifically, the sorbent compositions include a relatively small percentage of very fine particles, such as a small percentage of particles having a particle size of not greater than about 5 μm. The sorbent compositions are particularly useful for the treatment of a flue gas stream to remove mercury from the flue gas stream.

FIELD

This disclosure relates to the field of particulate sorbentcompositions, and in particular to carbonaceous sorbent compositionssuch as powdered activated carbon compositions having improved pneumaticconveyance capabilities.

BACKGROUND

Powdered activated carbon (“PAC”) is a highly amorphous form of carbonhaving an average particle size of about −80 mesh (e.g., not greaterthan about 177 μm). PAC is manufactured to have a high porosity, a smallaverage pore size and a high surface area, and is able to bind (e.g.,adsorb) many contaminant species from another substance, therebypurifying (e.g., decontaminating) the other substance.

Industrial applications of PAC include, but are not limited to, wastewater treatment, food purification, and the treatment of flue gas from aboiler (e.g., a coal boiler) to remove contaminants such as mercury fromthe flue gas. For many such industrial applications, PAC is shipped inbulk to an end user, such as by using trucks, rail shipment, or thelike. The PAC is unloaded from the truck or rail car and may be placedsubsequently in a storage unit (e.g., a storage silo). When the PAC isneeded, it is then conveyed to the point of use, e.g., to a watertreatment process or to a flue gas treatment process.

Often, the PAC is pneumatically conveyed such as from a rail car to astorage unit, from a rail car to a transportation truck, from atransportation truck to a storage unit, and/or from the storage unit tothe point of use. Pneumatic conveyance of PAC involves conveying the PACthrough an enclosed pipeline using a pressure differential and the flowof a gas (e.g., air) to suspend and move the PAC along the pipeline.Typically, the PAC is conveyed in a dilute phase, i.e., where theconveying system relies on the gas velocity to pick up and entrain theparticles. Pneumatic conveyance of PAC has many advantages over otherconveyance techniques. For example, pneumatic conveyance pipelines canbe arranged with bends to circumvent other equipment, and the system hasfew moving parts and is completely enclosed.

SUMMARY

Recently, it has been found that for some applications, and for thetreatment of flue gas streams in particular, particulate carbonaceoussorbent compositions (e.g., PAC-containing) having a reduced averageparticle size may be advantageous for the capture of contaminants suchas mercury (Hg) from a flue gas stream. In particular, sorbentcompositions that include PAC, having a relatively small averageparticle size, such as a median particle size (D50) of about 15 μm orless, may be advantageous for the removal of mercury from a flue gasstream.

However, it has been found that some PAC-containing sorbent compositionshaving a relatively small average particle size may be susceptible toflow interruptions and/or pressure fluctuations when being pneumaticallyconveyed in some situations, such as when being conveyed from a storageunit to the point of use (e.g., to the lances that inject thePAC-containing sorbent composition into the flue gas stream).Specifically, it has been found that the conveyance system mayexperience pressure spikes which can result in feeder and/or blower shutdown for a period of time. Such shut downs may result in an interruptionof the PAC flow to the flue gas stream and may lead to mercury emissionproblems. A need has been identified for a sorbent compositioncontaining a particulate sorbent such as PAC having a relatively smallmedian particle size and with good pneumatic conveyance properties,i.e., to reduce instabilities and interruptions during pneumaticconveyance of the sorbent composition.

It is one objective of the present disclosure to mitigate the problem ofpoor pneumatic conveyance of small sized particles, especially sorbentssuch as PAC. In one embodiment, a particulate sorbent composition isprovided which overcomes the limitations of pneumatic conveyance of somesmaller median particle size PACs, i.e., with median particle size ofabout 20 μm or less, such as 15 μm or less. It has been found that thepresence of large numbers of very fine particles, i.e., particles with aparticle size (diameter) of about 5 μm or less, may be related to thepneumatic conveyance issues sometimes experienced by the power plants.Typically, a batch of PAC with a D50 of about 20 μm or less has asignificant percentage of such very fine particles, such as greater thanabout 17 vol. % of such fine particles. It has been found thatcontrolling the percentage of such fine particles, e.g., by removingvery fine particles and/or otherwise sizing (e.g., classifying) thesorbent composition to reduce the number of very fine particles mayenable improved pneumatic transport capability.

In one embodiment, a particulate sorbent composition is provided thatincludes porous carbonaceous particles, wherein the particulate sorbentcomposition has a median particle size of not greater than about 20 μm,and has a particle size distribution wherein not greater than about 10vol. % of particles comprising the particulate sorbent composition havea particle size of not greater than about 5 μm.

In one characterization, the particulate sorbent composition haswell-controlled median particle size, such as not greater than about 18μm, not greater than about 15 μm, not greater than about 14 μm, or evennot greater than about 12 μm.

To enhance the pneumatic flow properties of sorbent compositions havingsuch a small median particle size, the concentration of very fine-sizedparticles in the composition is relatively low. In one characterization,not greater than about 5 vol. % of the particles comprising theparticulate sorbent composition have a particle size of not greater thanabout 5 μm.

The concentration of particles having a size of not greater than about 4μm may also be controlled. In one characterization, not greater thanabout 10 vol. % of the particles comprising the particulate sorbentcomposition have a particle size of not greater than about 4 μm. In yetanother characterization, not greater than about 5 vol. % of theparticles comprising the particulate sorbent composition have a particlesize of not greater than about 4 μm.

The concentration of particles having a particle size of not greaterthan 3 μm may also be controlled. In one characterization, not greaterthan about 8 vol. % of the particles comprising the particulate sorbentcomposition have a particle size of not greater than about 3 μm, and inanother characterization, not greater than about 4 vol. % of theparticles comprising the particulate sorbent composition have a particlesize of not greater than about 3 μm.

The concentration of particles having a particle size of not greaterthan 2 μm may also be controlled. In one characterization, not greaterthan about 5 vol. % of the particles comprising the particulate sorbentcomposition have a particle size of not greater than about 2 μm, such aswhere not greater than about 3 vol. % of the particles comprising theparticulate sorbent composition have a particle size of not greater thanabout 2 μm.

The concentration of particles having a particle size of not greaterthan 1 μm may also be controlled. In one characterization, the notgreater than about 2 vol. % of the particles comprising the particulatesorbent composition have a particle size of not greater than about 1 μm,such as where not greater than about 1 vol. % of the particlescomprising the particulate sorbent composition have a particle size ofnot greater than about 1 μm.

In another characterization, the porous carbonaceous particles of theparticulate sorbent composition are selected from the group consistingof activated carbon, reactivated carbon, carbonaceous char andcombinations thereof. In a particular characterization, the porouscarbonaceous particles comprise powdered activated carbon. For example,the powdered activated carbon may be derived from lignite coal.

The particulate sorbent compositions disclosed herein may have improvedpneumatic conveyance properties, e.g., as compared to similar sorbentcompositions having a higher concentration of fine-sized particles. Theimproved pneumatic conveyance properties may be described using one ormore powder flow characteristics that may be measured and quantifiedsuch as by using a powder rheometer. For example, the particulatesorbent composition may have a Basic Flow Energy of at least about 300mJ, such as a Basic Flow Energy of at least about 350 mJ, or even aBasic Flow Energy of at least about 400 mJ.

In another characterization, the particulate sorbent composition mayhave a Specific Energy of at least about 6 mJ/g, such as a SpecificEnergy of at least about 6.5 mJ/g.

In yet another characterization, the particulate sorbent composition mayhave an Aeration Energy of not greater than about 54 mJ, such as anAeration Energy not greater than about 20 mJ or even an Aeration Energyof not greater than about 10 mJ.

In another characterization, the particulate sorbent composition has anAeration Ratio of at least about 9, such as an Aeration Ratio of atleast about 20, such as an Aeration Ratio of at least about 30, or evenan Aeration Ratio of at least about 40.

In another characterization, the particulate sorbent compositioncomprises powdered activated carbon derived from lignite coal and has aConditioned Bulk Density of at least about 0.4 g/ml, such as aConditioned Bulk Density of at least about 0.46 g/ml, or even aConditioned Bulk Density of at least about 0.48 g/ml.

In another characterization, the particulate sorbent composition has apressure drop as measured by the Permeability test of not greater thanabout 55 mbar at an applied normal stress of 15 kPa and at an airvelocity of 0.5 mm/s. For example, the pressure drop as measured by thePermeability test may be not greater than about 40 mbar at an appliednormal stress of 15 kPa and at an air velocity of 0.5 mm/s. In anotherexample, the pressure drop as measured by the Permeability test is notgreater than about 30 mbar at an applied normal stress of 15 kPa and atan air velocity of 0.5 mm/s, such as a pressure drop as measured by thePermeability test of not greater than about 25 mbar at an applied normalstress of 15 kPa and at an air velocity of 0.5 mm/s. In one particularcharacterization, the pressure drop as measured by the Permeability testis not greater than about 20 mbar at an applied normal stress of 15 kPaand at an air velocity of 0.5 mm/s.

Another way to characterize the pneumatic flow properties is bymeasuring the Compressibility of the particulate sorbent composition. Inone characterization, the particulate sorbent composition has aCompressibility of not greater than about 24% at an applied normalstress of 15 kPa. In another characterization, the particulate sorbentcomposition has a Compressibility of not greater than about 20% at anapplied normal stress of 15 kPa. In a further characterization, theparticulate sorbent composition has a Compressibility of not greaterthan about 14% at an applied normal stress of 15 kPa.

The present disclosure also provides for methods for the treatment of aflue gas stream emanating from a boiler, comprising the step ofcontacting the flue gas stream with a particulate sorbent compositionaccording to any of the foregoing embodiments and characterizations.

In another embodiment, a method for the manufacture of a particulatesorbent composition is provided. The method may include the step ofcomminuting an intermediate particulate carbonaceous material to form acomminuted particulate carbonaceous material, the comminuted particulatecarbonaceous material having a median particle size of not greater thanabout 30 μm and a having a particle size distribution wherein greaterthan 10 vol. % of particles comprising the comminuted particulatecarbonaceous material have a particle size of not greater than 5 μm. Themethod may further include the step of sizing the comminuted particulatecarbonaceous material to produce a size-controlled particulate sorbentcomposition having a median particle size of not greater than about 30μm and a particle size distribution wherein not greater than about 10vol. % of particles comprising the size-controlled particulate sorbentcomposition have a particle size of less than about 5 μm.

In certain characterizations of this embodiment, the intermediateparticulate carbonaceous material comprises powdered activated carbon.For example, the intermediate particulate carbonaceous material may beformed by activating a carbon feedstock to form the powdered activatedcarbon.

In another characterization, the size-controlled particulate sorbentcomposition has a median particle size of not greater than about 25 μm,such as a median particle size of not greater than about 20 μm, such asa median particle size of not greater than about 18 μm, or even a medianparticle size of not greater than about 15 μm.

In certain characterizations, the sizing step includes removing from thecomminuted particulate sorbent composition at least a portion of theparticles comprising the comminuted particulate sorbent compositionhaving a particle size of less than 5 μm. For example, the removing stepmay include removing the portion of the particles comprising thecomminuted particulate sorbent composition having a particle size ofless than 5 μm using an air classifier.

In another characterization, the sizing step may include agglomeratingat least a portion of the particles comprising the comminutedparticulate sorbent composition having a particle size of less than 5μm.

In another characterization, not greater than about 10 vol. % of theparticles in the size-controlled particulate sorbent composition have aparticle size of not greater than about 5 μm. In yet anothercharacterization, not greater than about 5 vol. % of the particles inthe size-controlled particulate sorbent composition have a particle sizeof not greater than about 5 μm. In yet a further characterization, notgreater than about 2 vol. % of the particles in the size-controlledparticulate sorbent composition have a particle size of not greater thanabout 1 μm.

The enhanced pneumatic flow characteristics of the size-controlledparticulate sorbent composition may be characterized by a change inmeasurable flow properties of the composition. In one characterization,the Conditioned Bulk Density of the size-controlled particulate sorbentcomposition is greater than the Conditioned Bulk Density of thecomminuted particulate carbonaceous material. In a particularcharacterization, the Conditioned Bulk Density of the size-controlledparticulate sorbent composition is at least about 5% greater than theConditioned Bulk Density of the comminuted particulate carbonaceousmaterial. In yet another characterization, the Conditioned Bulk Densityof the size-controlled particulate sorbent composition is at least about10% greater than the Conditioned Bulk Density of the comminutedparticulate carbonaceous material.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of a system and method forpneumatically transporting and introducing PAC into a flue gas stream atan electric generating unit (EGU) or industrial boiler site.

FIG. 2 illustrates a flow sheet for the manufacture of a particulatesorbent composition in accordance with an embodiment of the presentdisclosure.

FIG. 3 illustrates the Permeability or pressure drop of a particulatesorbent composition disclosed herein with several comparative samples.

FIG. 4 illustrates the Compressibility of a particulate sorbentcomposition disclosed herein in with several comparative samples.

DETAILED DESCRIPTION

Various embodiments of a particulate sorbent composition are disclosedherein that have controlled particle size characteristics and thatdemonstrate improved pneumatic conveyance characteristics as compared tosimilar sorbent compositions where the particle size characteristics arenot carefully controlled.

In this regard, the particulate sorbent composition may have a medianparticle size of not greater than about 30 μm, such as not greater thanabout 20 μm, and a PSD wherein a relatively small volume percentage(vol. %) of very fine particles, e.g., a relatively small vol. % ofparticles having a size of not greater than about 5 μm, such as notgreater than about 15 vol. %, or even not greater than about 10 vol. %.Such a size-controlled particulate sorbent composition may be producedinherently in the manufacturing process or may be formed in a subsequentclassification process, for example where at least a portion of the veryfine-sized particles are removed, or alternately agglomerated. Theparticulate sorbent composition may be characterized as having certainquantifiable flow properties within desirable ranges, such as Basic FlowEnergy, Specific Energy, Conditioned Bulk Density, Aeration Energy,Aeration Ratio, Compressibility, and pressure drop, as measured in aPermeability test, the desired ranges being indicative of good pneumaticconveyance properties.

When a combustible material containing fixed carbon and volatile matter(e.g., coal or municipal waste) is combusted in a boiler (e.g., for thegeneration of electricity using a steam turbine), a flue gas is formedthat includes contaminants that originate from the combustible material.Such contaminants may include mercury (Hg), e.g., in concentrations offrom about 1 ppbw to 100 ppbw (parts per billion by weight).Environmental regulations limit the concentration of mercury in the fluegas that can be vented to the atmosphere. One method to capture mercuryfrom the flue gas is to contact the flue gas with a sorbent such as PAC,e.g., by injecting PAC into the flue gas stream. Sorbents such as PACare known to effectively remove heavy metals such as mercury from suchfluid streams.

FIG. 1 schematically illustrates a system 100 and method forpneumatically transporting and introducing a particulate sorbentcomposition into a flue gas stream 102 at a power plant or industrialboiler site, such as a coal-burning facility. A boiler 101 is configuredto burn coal and/or another material (e.g., municipal waste). Theburning of coal in the boiler 101 creates a flue gas stream 102 that mayinclude various components including gases (e.g., N₂, CO₂, O₂, NO_(x),SO_(x), etc.) and particulates (e.g., fly ash). The flue gas stream 102typically also includes heavy metals such as Hg that must be removedfrom the flue gas stream 102 before exiting the stack 104. In thisregard, sorbent compositions such as PAC may be injected into the fluegas stream 102 to capture (e.g., sequester) mercury.

The particulate sorbent composition may be stored in a silo or hopper105 prior to introduction to the flue gas stream 102. A blower 106forces air through an eductor 107 creating a venturi effect dispersingthe particulate sorbent composition into a conveyance line 108 andthrough injection lances 109 into the flue gas stream 102. Further, ascrew feeder (not shown) may transport the particulate sorbentcomposition from the silo or hopper 105 to the eductor 107. Aftercontacting the flue gas stream 102 with the particulate sorbentcomposition, the flue gas stream may be introduced to a particulatematter separation unit 103 to remove particulates (e.g., the particulatesorbent composition and fly ash) before exiting the stack 104. Thisparticulate matter separation unit 103 may be, for example, anelectrostatic precipitator. It will be appreciated by those skilled inthe art that the plant may include other devices not illustrated in FIG.1, such as a selective catalytic reduction unit (SCR), an air preheaterand the like, and may have numerous other configurations.

The particulate sorbent compositions disclosed herein may have improvedpneumatic conveyance properties to enhance the transport of the sorbentcompositions, such as through a conveyance line 108. The particulatesorbent compositions have controlled particle size characteristics, suchas where the vol. % of the particles in the compositions having a veryfine particle size (e.g., less than 5 μm) is reduced as compared toknown particulate sorbent compositions.

The sorbent compositions disclosed herein are selected for their abilityto sequester contaminants from a fluid stream, for example forsequestering heavy metals such as Hg from a flue gas stream. Usefulparticulate sorbent compositions will typically comprise particles thatare highly porous and have a high surface area. For example, theparticulate sorbent may comprise porous carbonaceous particles, zeoliteparticles, silica particles (including silica gel), alumina particles,clay particles (e.g., aluminosilicates) or combinations thereof. In aparticular embodiment, the sorbent composition includes porouscarbonaceous particles. Examples of porous carbonaceous particlesinclude PAC, reactivated carbon, carbonaceous char, and combinationsthereof. In one particular characterization, the sorbent compositionwill include PAC. In this regard, although the following discussionprimarily refers to the use of porous carbonaceous particles in thesorbent material, specifically PAC, the sorbent compositions of thepresent disclosure are not so limited. The PAC may be derived from avariety of sources (e.g., feedstocks), including anthracite coal,lignite coal, coconut shells, wood, and the like. In onecharacterization, the PAC is derived from a lignite coal feedstock,which generally has a higher mineral ash content than PAC derived fromanthracite coal.

The particulate sorbent composition may have a relatively small median(D50) particle size, such as a median particle size of not greater thanabout 30 μm. A smaller median particle size may be useful for manyapplications, such as for the treatment of a flue gas to remove mercury.In one characterization, the median particle size of the particulatesorbent composition may be not greater than about 25 μm, such as notgreater than about 20 μm, not greater than about 18 μm, or even notgreater than about 15 μm. Due to potential material handling issues, themedian particle size of the particulate sorbent composition may also beat least about 4 μm, such as at least about 6 μm, at least about 8 μm oreven at least about 10 μm. In one particular characterization, themedian particle size of the particulate sorbent composition is at leastabout 8 μm and is not greater than about 15 μm.

As is discussed above, it has been found that in addition to arelatively small median particle size, the particle size distribution(PSD) of the particulate sorbent composition should also bewell-controlled, particularly with regard to particles at the lower endof the size distribution. Such a controlled PSD may be characterized ina number of ways. In one characterization, the percentage (e.g., vol. %)of particles in the sorbent composition having a size (diameter) of notgreater than about 5 μm is not greater than a maximum vol. % of theparticles comprising the sorbent composition. For example, not greaterthan about 15 vol. % of the particles comprising the sorbent compositionmay have a particle size of not greater than about 5 μm, such as notgreater than about 10 vol. %, not greater than about 5 vol. %, or evennot greater than about 3 vol. %.

In another characterization of the sorbent compositions disclosedherein, the vol. % of particles comprising the particulate sorbentcomposition having a size of not greater than about 4 μm is not greaterthan a maximum vol. %. For example, not greater than about 10 vol. % ofthe particles comprising the particulate sorbent composition may have aparticle size of not greater than about 4 μm, such as not greater thanabout 5 vol. %, or even not greater than about 3 vol. %. In anothercharacterization, the vol. % of particles comprising the particulatesorbent composition having a size of not greater than 3 μm is notgreater than a maximum vol. %. For example, not greater than about 8vol. % of the particles comprising the particulate sorbent compositionmay have a particle size of not greater than about 3 μm, such as notgreater than about 4 vol. %, or even not greater than about 2 vol. %. Inanother characterization, the vol. % of particles comprising theparticulate sorbent composition having a size of not greater than 2 μmis not greater than a maximum vol. %. For example, not greater thanabout 5 vol. % of the particles comprising the particulate sorbentcomposition may have a particle size of not greater than 2 μm, such asnot greater than about 3 vol. % or even not greater than about 1 vol. %.In another characterization of the sorbent composition, the vol. % ofparticles comprising the particulate sorbent composition having a sizeof not greater than about 1 μm is not greater than a maximum vol. %. Forexample, not greater than about 2 vol. % of the particles comprising theparticulate sorbent composition may have a particle size of not greaterthan about 1 μm, such as not greater than about 1 vol. %, or even notgreater than about 0.5 vol. %.

Characterized another way, the vol. % of particles comprising theparticulate sorbent composition having a size of at least about 5 μm isgreater than a minimum vol. % of the particles. For example, at leastabout 85 vol. % of the particles comprising the particulate sorbentcomposition may have a particle size of at least about 5 μm, such as atleast about 90 vol. %, at least about 95 vol. %, or even at least about97 vol. %. In another characterization, the vol. % of particles having asize of at least about 4 μm is greater than a minimum vol. % of theparticles comprising the particulate sorbent composition. For example,at least about 90 vol. % of the particles comprising the particulatesorbent composition may have a particle size of at least 4 μm, such asat least about 95 vol. %, or even at least about 97 vol. %. In anothercharacterization, the vol. % of particles comprising the particulatesorbent composition having a size of at least about 3 μm is greater thana minimum vol. % of the particles. For example, at least about 92 vol. %of particles comprising the particulate sorbent composition may have aparticle size of at least 3 μm, such as at least about 96 vol. %, oreven at least about 98 vol. %. In another characterization, the vol. %of particles comprising the particulate sorbent composition having asize of at least about 2 μm is greater than a minimum vol. % of theparticles. For example, at least about 95 vol. % of the particlescomprising the particulate sorbent composition may have a particle sizeof at least about 2 μm, such as at least about 97 vol. %, or even atleast about 99 vol. %. In yet another characterization, the vol. % ofthe particles comprising the particulate sorbent composition having asize of at least about 1 μm is greater than a minimum vol. % of theparticles. For example, at least about 98 vol. %, such as at least about99 vol. %, or even at least about 99.5 vol. % of the particlescomprising the particulate sorbent composition may have a particle sizeof at least about 1 μm.

The particulate sorbent composition can also be characterized as havinga relatively narrow PSD. In this regard, the PSD may be characterized ashaving a median particle size, where the percentage of particles withina range around the median particle size is relatively high. For example,the PSD of the particulate sorbent composition may be characterized ashaving a median particle size in the range of from about 6 μm to about15 μm, where the D95 value (i.e., the particle size below which 95 vol.% of the particles fall) is not greater than about 30 μm, such as notgreater than about 28 μm. In another characterization, the D5 value(i.e., the particle size above which 95 vol. % of the particles fall) isat least about 3 μm, such as at least about 5 μm.

Median particle size and PSD of the sorbent compositions can bemeasured, for example, by using a Micrometrics Saturn DigiSizer II(Micrometrics Instrument Corporation, Norcross, Ga.), which is ahigh-definition digital particle size analyzer. This instrument employsa light scattering analysis technique that utilizes advanced digitaldetection technology.

Particulate sorbent compositions having the foregoing particle sizecharacteristics can be manufactured by controlling the manufacturingprocess to reduce the formation of very fine particles, and/or by sizing(e.g., classifying or agglomerating) the particulate sorbent material,e.g., by separating particles of a very fine size from the largerparticles. FIG. 2 is a flow sheet that illustrates an exemplary methodfor the manufacture of a particulate sorbent composition that includes aparticulate carbonaceous material, namely PAC. The manufacturing processbegins with a carbonaceous feedstock 201 such as coal, e.g., lignitecoal. In the manufacturing process, the feedstock 201 is subjected to anelevated temperature and one or more oxidizing gases under exothermicconditions for a period of time to activate the feedstock 201. Thespecific steps in the process include: (1) dehydration 202, where thefeedstock 201 is heated to remove the free and bound water, typicallyoccurring at temperatures ranging from 100° C. to 150° C.; (2)devolatilization 203, where free and weakly bound volatile organicconstituents are removed, typically occurring at temperatures above 150°C.; (3) carbonization 204, where non-carbon elements continue to beremoved and elemental carbon is concentrated and transformed into randomamorphous structures, typically occurring at temperatures ranging from350° C. to 800° C.; and (4) activation 205, where steam, air, or anotheroxidizing agent is added and pores are developed, typically occurring attemperatures above 800° C. The manufacturing process may be carried out,for example, in a multi-hearth or rotary furnace. The manufacturingprocess is not necessarily discrete and any two or more of the foregoingsteps can overlap and/or can use various temperatures, gases, andresidence times within each step to promote desired surface chemistryand physical characteristics of the manufactured intermediateparticulate carbonaceous material.

After activation 205, the intermediate particulate carbonaceous materialtypically contains many agglomerates and typically has a median particlesize that is too large to be used in many sorbent applications, such asfor the treatment of a flue gas. In this regard, the intermediateparticulate carbonaceous material may be subjected to a comminution step206 to reduce the particle size (e.g., the median particle size) of theintermediate particulate carbonaceous material and form a comminutedparticulate carbonaceous material having a desired median particle size.Comminution 206 may occur, for example, in a mill such as a roll mill,jet mill, classifier mill, or other like device. Typically, comminution206 of the intermediate particulate carbonaceous material is carried outunder conditions (e.g., for a period of time) to form a comminutedparticulate carbonaceous material having a median particle size of notgreater than about 30 μm. In one characterization, the comminuting stepis carried out under conditions such that the comminuted particulatecarbonaceous material has a median particle size of not greater thanabout 25 μm, such as not greater than about 20 μm, not greater thanabout 18 μm, or even not greater than about 15 μm.

However, typical comminution methods also lead to the formation of arelatively high percentage of particles having a very small particlesize. For example, greater than 10 vol. %, such as greater than 15 vol.% or even greater than 20 vol. % of the comminuted particles from thecomminution step 206 may have a particle size of not greater than 5 μm.As is discussed above, such concentrations of very fine-sized particlesmay inhibit the pneumatic flow of sorbent compositions containing theparticles.

In one characterization, the comminution step 206 may be controlled toreduce the formation of particles having a very fine particle size(e.g., not greater than about 5 μm). Alternatively, or in addition tosuch control, the manufacturing process (e.g., prior to comminution) maybe controlled to yield an end product having the desired particle sizeproperties, such as by controlling the particle size properties of theinitial feedstock 201.

In the event that manufacturing conditions result in a greater number ofvery fine-sized particles than is desired, a sizing step 207 may becarried out to reduce the concentration of such very fine particles inthe comminuted particulate sorbent composition. For example, thecomminuted particulate carbonaceous material may be subjected to asizing step 207 that includes selectively agglomerating at least aportion of the fine-sized particles to form larger sized particles,thereby reducing the concentration of fine-sized particles. For example,the selective agglomeration step may include the selective agglomerationof particles having a particle size of less than about 5 μm.

In another characterization, the sizing step 207 may include removingfrom the comminuted particulate sorbent composition at least a portionof the fine-sized particles. For example, the sizing step 207 mayinclude removing at least a portion of particles having a particle sizeof less than 3 μm, such as by removing at least a portion of particleshaving a particle size of less than 4 μm or even less than 5 μm. Theselective removal of such particles may be carried out using an airclassifier, screen/mesh classification (e.g., vibrating screens), orcentrifugation, for example.

In either event, the sizing step 207 may be carried out to formparticulate sorbent composition (e.g., a size-controlled particulatesorbent composition) having the particle size characteristics describedabove.

The sorbent compositions described herein may further include otheradditives to enhance the efficacy of the sorbent compositions in aselected application, such as for the treatment of a flue gas stream toremove mercury. Examples of such additives include, but are not limitedto, oxidizing agents, acid gas agents, and flow agents.

By way of example, the sorbent compositions may include one or moreoxidizing agents that may improve the adsorption of mercury from a fluegas stream. Oxidizing agents may include halogen salts such as inorganichalogen salts, which may include bromine compounds such as bromides,bromates or hypobromites, iodine compounds such as iodides, iodates orhypoiodites, or chlorine compounds such as chlorides, chlorates orhypochlorites. The inorganic halogen salt may be an alkali metal or analkaline earth element containing halogen salt where the inorganichalogen salt is associated with an alkali metal such as lithium, sodium,and potassium or alkaline earth metal such as magnesium, and calcium.Non-limiting examples of inorganic halogen salts include alkali metaland alkali earth metal counterions, such as calcium hypochlorite,calcium hypobromite, calcium hypoiodite, calcium chloride, calciumbromide, calcium iodide, magnesium chloride, magnesium bromide,magnesium iodide, sodium chloride, sodium bromide, sodium iodide,potassium tri-chloride, potassium tri-bromide, potassium tri-iodide, andthe like. The oxidizing agents may be included in the composition at anyconcentration, and in some embodiments, no oxidizing agent may beincluded in the compositions embodied by the invention.

In some embodiments, the sorbent composition may include an acid gasagent such as, for example, an alkaline compound. Numerous alkalineagents are known in the art and currently used to remove sulfur oxidespecies from flue gas and any such alkaline agent may be used in theinvention. For example, in various embodiments, the alkaline additivemay be alkali oxides, alkaline earth oxides, hydroxides, carbonates,bicarbonates, phosphates, silicates, aluminates, and combinationsthereof, and in certain embodiments, the alkaline agent may be calciumcarbonate (CaCO₃), calcium oxide (CaO), calcium hydroxide (Ca(OH)₂);magnesium carbonate (MgCO₃); magnesium hydroxide (Mg(OH)₂) magnesiumoxide (MgO), sodium carbonate (Na₂CO₃), sodium bicarbonate (NaHCO₃),trisodium hydrogendicarbonate dihydrate (Na₃(CO₃)(HCO₃).2H₂O), andcombinations thereof.

In one particular example, the acid gas agent is a trivalent or higherGroup 3 to Group 14 metal-containing compound selected from the groupconsisting of a carbonate, an oxide, a hydroxide, an ionic saltprecursor to a hydroxide and combinations thereof. For example, thetrivalent or higher metal may be selected from Group 13 to Group 14metals, and in certain characterizations the trivalent or higher metalis a Group 13 metal. For example, the trivalent or higher metal may bealuminum. In other characterizations, the trivalent or higher metal maybe tin. The metal-containing compound may comprise an anion and acation, where the cation includes the trivalent or higher metal. Themetal-containing compound may also be a metal oxide, for example SnO₂.The metal-containing compound may also be a metal hydroxide, such asaluminum hydroxide. The metal-containing compound may also be an ionicsalt precursor to a metal hydroxide, such as an ionic salt that includesa polyatomic anion where the trivalent or higher Group 3 to Group 14metal is a component of the polyatomic anion. The polyatomic anion maybe an oxoanion and the metal may be aluminum. For example, the ionicsalt may be sodium aluminate or sodium stannate. Such acid gas agentsare disclosed in more detail in commonly-owned U.S. patent applicationSer. No. 14/142,636 by Wong et al., which is incorporated herein byreference in its entirety.

The sorbent compositions disclosed herein may also include flow agentsto further enhance the flow properties of the sorbent composition.Examples include, but are not limited to, flake-like particles such asphyllosilicate minerals (e.g., mica or talc) or graphite. Such flowagents are disclosed in more detail in commonly-owned U.S. patentapplication Ser. No. 14/145,731 by McMurray et al., which isincorporated herein by reference in its entirety. Other examples of flowagents include precipitated silica.

As is noted above, the sorbent compositions disclosed herein may haveimproved pneumatic conveyance properties as compared to known sorbentcompositions, particularly when the sorbent composition (e.g., the PAC)has a small median particle size (e.g., about 20 μm or less). Toquantify this result, various powder characteristics can bequantitatively measured to indicate such improvements, including BasicFlow Energy (“BFE”), Specific Energy (“SE”), Conditioned Bulk Density(“CBD”), Aeration Energy (“AE”), Aeration Ratio (“AR”), pressure drop,as measured in a Permeability test, and/or Compressibility of thesorbent composition.

These powder characteristics can be measured using a powder rheometer,for example using a Freeman Technology 4 (“FT4”) Powder Rheometer,available from Freeman Technology (Worcestershire, United Kingdom). TheFT4 Powder Rheometer is capable of quantitatively measuring theflowability characteristics of particulate compositions, and thesemeasurements can be utilized to predict the characteristics of theparticulate composition when being pneumatically conveyed, e.g., in adilute phase. The FT4 Powder Rheometer includes a container for holdinga powder sample and a rotor having a plurality of blades that isconfigured to move in the axial direction (e.g., vertically) through thepowder sample while rotating the blades relative to the container. See,for example, U.S. Pat. No. 6,065,330 by Freeman et al., which isincorporated herein by reference in its entirety.

BFE and SE are determined by the FT4 Powder Rheometer using theStability and Variable Flow Rate method (“the SVFR method”). The SVFRmethod includes seven test cycles using a stability method and four testcycles using a variable flow rate method, where each test cycle includesa conditioning step before the measurement is taken. The conditioningstep homogenizes the sorbent composition by creating a uniform lowstress packing of particles throughout the sample, which removes anystress history or excess entrained air prior to the measurement. Thestability method includes maintaining the blade tip speed at about 100millimeters per second (mm/s) during the test cycles, whereas thevariable flow rate method involves four measurements using differentblade tip speeds, namely about 100 mm/s, about 70 mm/s, about 40 mm/sand about 10 mm/s. The test measures the energy required to rotate theblade through the powder from the top of the vessel to the bottom and torotate the blade through the powder from the bottom to the top of thevessel.

BFE is the total energy measured during the seventh cycle during thestability method measurements of the SVFR method described above (i.e.,at a tip speed set at 100 mm/s) while the blade is rotating from the topof the vessel to the bottom. The BFE is a measurement of the energyrequired to establish a particular flow pattern in a (conditioned)powder, which is established by a downward counter-clockwise motion ofthe blade that puts the powder under a compressive stress. The BFE, whenconsidered in conjunction with other powder characteristics, can be usedto predict the pneumatic conveyance properties of the sorbentcomposition. For some particulate compositions, the lower the BFE, themore easily the sorbent composition can be made to flow in a regular andinvariable manner, e.g., without significant variations in linepressure. However, for the sorbent compositions having a small volume ofvery fine particles disclosed herein, the composition will be relativelyuncompressible due to a lack of entrained air that would otherwisesurround the fine particles. That is, the particulate compositionsdisclosed herein begin in a relatively efficient packing state, andtherefore blade movement in the rheometer is not accommodated by the airpockets that exist in more cohesive powders, i.e., powders containinghigher levels of very fine particles. This results in more contactstress, and therefore a higher BFE than powders that include many veryfine particles.

Thus, the particulate sorbent compositions disclosed herein may becharacterized as having a BFE of at least about 275 millijoules (mJ),such as at least about 300 mJ, at least about 350 mJ, or even at leastabout 400 mJ.

The SE is the converse of the BFE, in the sense that the flow pattern isgenerated by an upward, clockwise motion of the blade in the powderrheometer, generating gentle lifting and low stress flow of thecomposition. Specifically, SE is the total energy measured during theseventh cycle during the stability method measurements of the SVFRmethod described above (i.e., at a tip speed set at −100 mm/s) while theblade is rotating from the bottom of the vessel to the top. As with theBFE, the reduced number of very fine particles in the present sorbentcompositions will create an efficient particle packing state and the SEwill be increased as compared to the same or similar powder thatincludes a larger volume of very fine particles.

In this regard, the particulate sorbent compositions disclosed hereinmay have a SE of at least about 6 millijoules per gram (mJ/g), such asat least about 6.5 mJ/g, or even at least about 6.7 mJ/g.

Conditioned Bulk Density (“CBD”) may also be measured with the FT4Powder Rheometer using the SVFR method. Bulk density may be measured atvarious packing conditions, and measuring the mass of a precise volumeof conditioned powder provides the CBD. The CBD of a sorbent compositionhaving a low percentage of very fine particles, e.g., that has beenclassified to remove very fine particles, will be higher than the CBD ofthe same powder that includes a higher percentage of very fine particles(e.g., that has not been classified to remove very fine particles).

Thus, a higher CBD may indicate the presence of fewer very fine-sizedparticles (e.g., <5 μm) in the composition. In this regard, theparticulate sorbent compositions disclosed herein, particularly thosecomprising PAC derived from lignite coal, may be characterized as havinga CBD of at least about 0.4 g/ml, such as at least about 0.46 g/ml, oreven at least about 0.48 g/ml. Characterized another way, when theparticulate sorbent composition is manufactured using a sizing step toreduce the number of very fine-sized particles (e.g., as is describedabove with respect to FIG. 2), the particulate sorbent composition(e.g., a size-controlled particulate sorbent composition) may have a CBDthat is greater than the CBD of the composition before sizing (e.g.,greater than the comminuted particulate carbonaceous material). In onecharacterization, the CBD of the size-controlled particulate sorbentcomposition is at least about 5% greater than the comminuted particulatecarbonaceous material, such as at least about 10% greater.

AE is a measure of how much energy is required for a powder to becomeaerated, which is directly related to the cohesive strength of thepowder (i.e., the tendency for particles to “stick” together). AE may bedetermined in the FT4 Powder Rheometer using the aeration test, whichprovides a precise air velocity to the base of the vessel containing thepowder and measures the change in energy required to rotate the bladesthrough the powder sample as the air velocity changes. During theaeration test, the air velocity (e.g., in mm/s) is varied over a rangeof from about 0.2 millimeters per second (mm/s) to about 2.0 mm/s, e.g.,in 0.2 mm/s increments. The reported AE value is the measured energy at1.0 mm/s.

As a general rule, the less cohesive, and therefore more easilyfluidized, the sorbent composition, the lower the AE, and the moreeasily the sorbent composition can be pneumatically conveyed. In thisregard, the particulate sorbent compositions disclosed herein may havean AE of not greater than about 54 mJ, such as not greater than about 30mJ, not greater than about 20 mJ, or even not greater than about 10 mJ.

Another measure of cohesiveness is the AR, which is a unitless quantityexpressing the ratio of AE at zero air velocity to the AE at a given airvelocity. For purposes of this disclosure, including the claims, an airvelocity of 1.0 mm/s for the AE is used to calculate the AR. If the ARis 1, then there is very little change in AE as the air velocityincreases, and the composition is said to be cohesive. Powders with ARsof 2 to 20 are said to have average sensitivity to aeration, and mostpowders fall within this range. At an AR above 20, powders areconsidered sensitive to aeration. As a general rule, the larger the ARand the lower the AE, the less cohesive and therefore more easilyfluidized and pneumatically conveyed the powder.

In this regard, the particulate sorbent compositions disclosed hereinmay have an AR of at least about 9, such as at least about 20, at leastabout 30, or even at least about 40.

The pressure drop, measured by the Permeability test, is a measure ofthe resistance to air flow between particles and through the powder bed.Pressure drop may be measured with the FT4 Powder Rheometer using aPermeability test which measures the pressure drop across the powder bedas a function of the applied normal stress (kinematic) in kPa. The lessthe pressure drop that is measured, the more likely the powder is toflow when pneumatically conveyed. Typically, a powder with lowpermeability will generate a pressure drop of over 50 mbar from at about15 kPa and at an air velocity of 0.5 mm/s. In contrast, permeablepowders will barely register a pressure drop at this air velocity.

The particulate sorbent compositions disclosed herein may have apressure drop as measured by the Permeability test that does not exceedabout 55 mbar at an applied normal stress of 15 kPa and at an airvelocity of 0.5 mm/s. In certain characterizations, the pressure dropdoes not exceed about 40 mbar under the same conditions, such as notexceeding about 30 mbar, not exceeding about 25 mbar or even notexceeding about 20 mbar at an applied normal stress of 15 kPa and at anair velocity of 0.5 mm/s.

Compressibility is another characteristic that can affect flowabilityand may be measured by the FT4 Powder Rheometer using thecompressibility test. Compressibility is a measure of how bulk densityincreases on compression. The less compressible a powder is, the morelikely it is to flow when pneumatically conveyed because there are morepaths for air. In other words, free flowing materials tend to beinsensitive to compressibility. A highly compressible composition withlower flowability would be characterized by a compressibility of about40% at 15 kPa for example; and a more flowable sample would have acompressibility of less than 20% at 15 kPa.

As such, the compressibility of the particulate sorbent compositionsdescribed herein may be not greater than about 20%, or even not greaterthan about 15%, at an applied stress of 15 kPa.

EXAMPLES

Samples of sorbent compositions are prepared to evaluate the pneumatictransport capability of the sorbent compositions disclosed herein ascompared to known sorbents. Comparative Sample 1 has a median particlesize of about 17 μm and particles less than 5 μm were about 17 vol. % ofthe sample. Comparative Sample 2 has a median particle size of about 10μm and particles less than 5 μm were about 26 vol. %. Comparative Sample3 has a median particle size of about 11 μm and particles less than 5 μmare about 24 vol. %. Sample 3 also includes about 4.5 vol. % of abromide salt. Sample 4 is in accordance with the present disclosure andhas a median particle size of about 13 μm and particles less than 5 μmare about 3 vol. %.

Table 1 indicates particle size characteristics for these samples.

TABLE 1 Particle Size Characteristics Median Vol. % Vol. % Vol. % Vol. %Vol. % particle Finer Finer Finer Finer Finer Sample size than than thanthan than D5 D95 Designation (μm) 5 μm 4 μm 3 μm 2 μm 1 μm (μm) (μm)Comparative 17 17.1 13.7 10.1 6.2 2.4 1.66 51.9 Sample 1 Comparative 1026.5 21.6 16.3 10.4 3.9 1.20 32.5 Sample 2 Comparative 11 24.4 19.7 15.010.5 5.0 1.00 29.7 Sample 3 Sample 4 13 3.2 1.6 0.9 0.5 0.0 5.65 27.0

Table 2 summarizes BFE (Basic Flow Energy), SE (Specific Energy), CBD(Conditioned Bulk Density), AE, AR, Compressibility (Comp.) and PressureDrop values measured for the samples.

TABLE 2 Powder Characteristics of Various Samples BFE SE CBD AE Comp.Pressure Drop Sample (mJ) (mJ/g) (g/ml) (mJ) AR (%) (mbar) Comparative229.15 4.97 0.462 20.42 8.76 14-23 55 Sample 1 Comparative 195.73 4.480.376 27.20 5.18 15-24 70 Sample 2 Comparative 260.53 6.31 0.380 54.533.41 16-28 90 Sample 3 Sample 4 418.75 6.92 0.484 8.15 48.29  9-13 20

Referring to Table 2, it is known that PAC having a larger medianparticle size (Comparative Sample 1) flows well when pneumaticallyconveyed. It is also known that Comparative Sample 3, having a reducedparticle size, may experience pneumatic flow issues in some situations.It can be seen that Comparative Sample 1 has a lower BFE, a lower SE,lower AE, lower Compressibility, and a lower pressure drop thanComparative Sample 3. A lower AE may be indicative that ComparativeSample 1 is less cohesive than Comparative Sample 3. Finer powdersexhibit more cohesive behavior, and so given the relative D50s, thismakes sense. In general, it is known that a powder with a larger AR andsmaller AE is less cohesive. Comparative Sample 1 exhibits both a largerAR and smaller AE than Comparative Sample 3, and this is therefore inalignment with what would be expected.

Sample 4 shows both the lowest AE, and highest AR. This is indicative ofvery good pneumatic conveyance properties for this composition.

Pressure drop is derived from the Permeability test as described above,and is greatly affected by cohesivity, size distribution, etc. Ingeneral, finer powders are less permeable, and therefore experience ahigher pressure drop. This is due to the way the fine particles pack thespaces (voids) between the larger particles. Consequently, it is inalignment with expectations that Comparative Sample 1 has a lowerpressure drop than Comparative Sample 3.

Sample 4 shows the lowest pressure drop across the powder bed,indicating high permeability. This is likely due to the absence of alarge number of very fine particles in accordance with the presentdisclosure, and indicates very good flow properties.

Compressibility measures the change in density of the powder as a normalstress is applied. Compressibility is also affected by particle sizedistribution, cohesivity, etc. In general, finer powders are morecohesive, and therefore more compressible. Therefore it is to beexpected that Comparative Sample 3 is more compressible than ComparativeSample 1.

Sample 4 experiences the lowest compressibility of the bulk powder. Itcan therefore be predicted that this composition experiences very goodflow properties.

CBD is a factor describing the relationship between mass and volume, andis affected by true density, particle size and distribution, cohesion,etc. The interaction of all these factors controls how volume and voidspace interact. The CBD creates a repeatable condition wherein thepowder is in a homogeneous, low stress packing state. The fact thatComparative Sample 1 has a higher CBD than Comparative Sample 3 is mostlikely indicative of the differences between particle size and particlesize distributions. The more cohesive finer particles in ComparativeSample 3 are likely creating more void space, and lower density in thepowder.

Sample 4, with the finer particles removed, has removed the majority ofthe void space. Consequently Sample 4 shows the highest CBD, with 27%higher CBD than sample 3, and 29% higher CBD than sample 2.

FIG. 3 illustrates the pressure drop across a powder bed (mBar) as afunction of applied normal stress, kinematic (kPa) from 2 kPa to 15 kPa.The pressure drop is measured using an FT4 powder rheometer from FreemanTechnology, Inc. Manufacturer's instructions are followed except an airvelocity of 0.5 mm/s was used. Table 2, above, indicates pressure dropdata measured for each sample at 15 kPa and at an air velocity of 0.5mm/s.

FIG. 4 illustrates compressibility of the samples. Compressibility ismeasured using the FT4 powder rheometer as described above.Compressibility is measured over a pneumatic applied normal stress rangeof 4 kPa to 15 kPa. As is illustrated by FIG. 4, Sample 4 according tothe present disclosure has the lowest compressibility over the entirerange of applied normal stress, and has a value of about 13% at anapplied normal stress of 15 kPa. In contrast, the comparative sampleshave a Compressibility of well over 20% at an applied normal stress of15 kPa.

As is illustrated by the above data, there may be no one exactmeasurement that best predicts flowability of a composition. How exactlymedian particle size affects flowability may not completely beunderstood. However, it has been found that reducing the percentage ofparticles smaller than 5 μm in a sorbent composition significantlyincreases flowability as evidenced by favorable changes incharacteristics identified in Table 2 above of compositions of matter,especially sorbents such as PAC.

While various embodiments have been described in detail, it is apparentthat modifications and adaptations of those embodiments will occur tothose skilled in the art. However, is to be expressly understood thatsuch modifications and adaptations are within the spirit and scope ofthe present disclosure.

What is claimed is:
 1. A particulate sorbent composition, theparticulate sorbent composition comprising porous carbonaceous particlesselected from the group consisting of activated carbon, reactivatedcarbon, carbonaceous char and combinations thereof, wherein theparticulate sorbent composition has a median particle size of notgreater than about 20 μm, and a particle size distribution wherein notgreater than about 10 vol. % of particles comprising the particulatesorbent composition have a particle size of not greater than about 5 μm.2. The particulate sorbent composition of claim 1, wherein theparticulate sorbent composition has a median particle size of notgreater than about 18 μm.
 3. The particulate sorbent composition ofclaim 1, wherein the particulate sorbent composition has a medianparticle size of not greater than about 15 μm.
 4. The particulatesorbent composition of claim 1, wherein the particulate sorbentcomposition has a median particle size of not greater than about 12 μm.5. The particulate sorbent composition of claim 1, wherein not greaterthan about 5 vol. % of the particles comprising the particulate sorbentcomposition have a particle size of not greater than about 5 μm.
 6. Theparticulate sorbent composition of claim 1, wherein not greater thanabout 8 vol. % of the particles comprising the particulate sorbentcomposition have a particle size of not greater than about 3 μm.
 7. Theparticulate sorbent composition of claim 1, wherein not greater thanabout 5 vol. % of the particles comprising the particulate sorbentcomposition have a particle size of not greater than about 2 μm.
 8. Theparticulate sorbent composition of claim 1, wherein not greater thanabout 2 vol. % of the particles comprising the particulate sorbentcomposition have a particle size of not greater than about 1 μm.
 9. Theparticulate sorbent composition of claim 1, wherein the porouscarbonaceous particles comprise powdered activated carbon.
 10. Theparticulate sorbent composition of claim 9, wherein the powderedactivated carbon is derived from lignite coal.
 11. The particulatesorbent composition of claim 1, wherein the particulate sorbentcomposition has a Basic Flow Energy of at least about 300 mJ.
 12. Theparticulate sorbent composition of any of claim 1, wherein theparticulate sorbent composition has a Basic Flow Energy of at leastabout 350 mJ.
 13. The particulate sorbent composition of claim 1,wherein the particulate sorbent composition has a Specific Energy of atleast about 6 mJ/g.
 14. The particulate sorbent composition of claim 1,wherein the particulate sorbent composition has a Specific Energy of atleast about 6.5 mJ/g.
 15. The particulate sorbent composition of claim1, wherein the particulate sorbent composition has an Aeration Energy ofnot greater than about 54 mJ.
 16. The particulate sorbent composition ofclaim 1, wherein the particulate sorbent composition has an AerationEnergy of not greater than about 20 mJ.
 17. The particulate sorbentcomposition of claim 1, wherein the particulate sorbent composition hasan Aeration Ratio of at least about
 9. 18. The particulate sorbentcomposition of claim 1, wherein the particulate sorbent composition hasan Aeration Ratio of at least about
 20. 19. The particulate sorbentcomposition of claim 10, wherein the particulate sorbent composition hasa Conditioned Bulk Density of at least about 0.4 g/m l.
 20. Theparticulate sorbent composition of claim 10, wherein the particulatesorbent composition has a Conditioned Bulk Density of at least about0.46 g/ml.
 21. The particulate sorbent composition of claim 1, whereinthe particulate sorbent composition has a pressure drop as measured bythe Permeability test of not greater than about 55 mbar at an appliednormal stress of 15 kPa and at an air velocity of 0.5 mm/s.
 22. Theparticulate sorbent composition of claim 1, wherein the particulatesorbent composition has a pressure drop as measured by the Permeabilitytest of not greater than about 40 mbar at an applied normal stress of 15kPa and at an air velocity of 0.5 mm/s.
 23. The particulate sorbentcomposition of claim 1, wherein the particulate sorbent composition hasa Compressibility of not greater than about 24% at an applied normalstress of 15 kPa.
 24. The particulate sorbent composition of claim 1,wherein the particulate sorbent composition has a Compressibility of notgreater than about 20% at an applied normal stress of 15 kPa.
 25. Amethod for the treatment of a flue gas stream emanating from a boiler,comprising the step of contacting the flue gas stream with theparticulate sorbent composition recited in claim
 1. 26. The particulatesorbent composition of claim 1, wherein the particulate sorbentcomposition further comprises a halogen-containing compound.
 27. Aparticulate sorbent composition, the particulate sorbent compositioncomprising porous carbonaceous particles selected from the groupconsisting of activated carbon, reactivated carbon, carbonaceous charand combinations thereof, wherein the particulate sorbent compositionhas a median particle size of not greater than about 12 μm, and aparticle size distribution wherein not greater than about 10 vol. % ofparticles comprising the particulate sorbent composition have a particlesize of not greater than about 5 μm, and wherein the particulate sorbentcomposition further comprises a halogen-containing compound.
 28. Theparticulate sorbent composition of claim 27, wherein the porouscarbonaceous particles comprise powdered activated carbon.